nfp: update ethtool reporting of pauseframe control

[ Upstream commit 9fdc5d85 ]

Pauseframe control is set to symmetric mode by default on the NFP.
Pause frames can not be configured through ethtool now, but ethtool can
report the supported mode.

Fixes: 265aeb51 ("nfp: add support for .get_link_ksettings()")
Signed-off-by: Fei Qin <fei.qin@corigine.com>
Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>